Relaxor Ferroelectric System Research Articles

Giant electrocaloric response in compositional manipulated BaTiO3 relaxor–ferroelectric system

The compositional manipulation of the multiphase coexistence in relaxor–ferroelectrics has been reported to be an effective approach to generate the giant electrocaloric effect. In this work, we systemically investigate the temperature-dependent electrocaloric effect in BaZr0.18Ti0.82O3–BaSn0.11Ti0.89O3 relaxors, where Zr and Sn are introduced into BaTiO3 to develop the multiphase coexistence at the ferroelectric–paraelectric transition. Through the direct measurement by the heat flux sensor, a large temperature change around 4 K under an electric field of 10 MV m−1, combined with a broad temperature span (20 °C–60 °C), has been observed. For comparison, the electrocaloric properties are also indirectly deduced based on Maxwell equations and Landau–Ginzburg–Devonshire phenomenological theory, and the validity of the indirect methods in this relaxor–ferroelectric system has been discussed. This work would shed light on developing giant electrocaloric materials with a wide operating temperature range.

Structure and physical properties of solid solutions based on the PbMn1/3Nb2/3O3 relaxor ferroelectric

We report on structural, dielectric and vibrational properties of the relaxor–ferroelectric system (1 − x)·Pb(Mn1/3Nb2/3)O3 – x·(PbTiO3) in the concentration range of 0.15 ≤ x ≤ 0.25. The range corresponds to a morphotropic (MPT) phase boundary between the rhombohedral R3m and tetragonal P4mm phases of the solid solution. The non-doped Pb(Mn1/3Nb2/3)O3 was of the R3m space group, demonstrating smeared phase transitions and relaxor behavior. Increasing concentration of the dopant led to a gradual suppression of the relaxor behavior with occurrence of a sharp first-order phase transition.

High energy density, high efficiency and excellent temperature stability of lead free Mn–doped BaTiO3–Bi(Mg1/2Zr1/2)O3 ceramics sintered in a reducing atmosphere

Dielectric ceramics capacitors are of great interest duo to the improved energy-storage performance and temperature stability. However, to lower the cost and achieve mass production, the co-sintering of dielectric ceramics with base metals (such as Ni, Cu) is a huge challenge, since the co-sintering requires a reducing atmosphere to prevent the oxidization of base metals. Here in this work, the multivalence element Mn is doped into a relaxor ferroelectric ceramic system, i.e. 0.85BaTiO3-0.15Bi(Mg1/2Zr1/2)O3 (BT-BMZ) ceramics through a conventional solid-state reaction method to realize the reducing atmosphere sintering. Effects of MnCO3 contents (0.05–0.25 wt%) on the energy-storage properties, temperature stabilities and electrical structures of the relaxor-ferroelectric BT-BMZ ceramics are investigated. The optimal energy-storage performance is found in 0.10 wt% MnCO3 doped BT-BMZ ceramics, with a high discharge energy density of 1.61 J/cm3 and an ultrahigh energy efficiency of 94.3% under the applied electric field of 230 kV/cm. Further, the variation in energy density is less than 15% over the temperature range from 25 to 140 °C under 120 kV/cm. Additionally, the impedance spectroscopy is used to analyze the insulation mechanism of these reducing-atmosphere-sintered Mn-doped BT-BMZ ceramics.

A coupled microstructural-structural mechanism governing thermal depolarization delay in Na0.5Bi0.5TiO3-based piezoelectrics

Driven by environmental concerns and governmental directives, a sustained research effort in the last decade and half has led to the development of lead-free alternatives which can potentially replace the commercial lead-based piezoceramics in niche applications. Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics have found acceptance as promising lead-free transducers in high power ultrasonic devices. An issue of concern however is the low depolarization temperature which limits the device's tolerance for temperature rise during operation. While several strategies have been reported to improve thermal depolarization in NBT-based piezoceramics, there is a lack of consensus regarding the most fundamental factor/mechanism which enhances the depolarization temperature. In this paper we unravel a coupled microstructural-structural mechanism which controls the thermal depolarization in NBT-based piezoceramics. First, we demonstrate the phenomenon of a considerable increase in the depolarization temperature, without significantly losing the piezoelectric property in unmodified NBT by increasing the grain size. We then establish a grain size controlled structural mechanism and demonstrate that the rise in depolarization temperature is primarily associated with the bigger grains allowing relatively large lattice distortion to develop in the poling stabilized long range ferroelectric phase. We reconfirmed the validity of this mechanism in the model morphotropic phase boundary (MPB) composition 0.94Na0.5Bi0.5TiO3-0.06BaTiO3. For the sake of generalization, we demonstrate that the same mechanism is operative in another lead-based relaxor-ferroelectric system 0.62PbTiO3-0.38Bi(Ni0.5Hf0.5)O3. Our study provides the fundamental structural basis for understanding thermal depolarization delay in relaxor ferroelectric based piezoceramics.

Electric field effect on short-range polar order in a relaxor ferroelectric system.

Short-range polar order in the relaxor ferroelectric material (PMN-28PT) have been studied using neutron diffuse scattering. An external electric field along the direction can affect the diffuse scattering in the low temperature rhombohedral/monoclinic phase. Diffuse scattering intensities associated with short-range polarizations are partially suppressed, while those arising from polarizations are enhanced. On the other hand, short-range polar order along other equivalent directions, i.e., , , [011], and directions, are virtually unaffected by the field. Our results, combined with previous work, strongly suggest that most parts of short-range polar order in PMN-xPT relaxor systems are robust in the low temperature phase, where they couple strongly to ferroelectric polarizations of the surrounding ferroelectric domains, and would only respond to an external field indirectly through ferroelectric domain rotation.

Lead–Oxygen Bond Length Distributions of the Relaxor Ferroelectric 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 from 207Pb Nuclear Magnetic Resonance

We investigate changes in the local environment of 207Pb sites in the relaxor ferroelectric 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 using variable temperature magic angle spinning nuclear magnetic resonance. We observe a Gaussian distribution of 207Pb chemical shifts with a mean chemical shift of −1469 ± 8 ppm and a standard deviation of 229 ± 8 ppm at 306 K and a mean chemical shift of −1410 ± 1 ppm and a standard deviation of 275 ± 1 ppm at 117 K. This corresponds to a decrease in the mean Pb–O bond length and a concurrent decrease in the effective coordination number from 6 to 5.8. An observed change in the asymmetry parameter from 0.4 to 0.8 for deshielded sites as well as a change in the shielding anisotropy of 300 ppm compared to 180 ppm for the more shielded resonances, indicating that the lead sites experience a more asymmetric environment at low temperature. Our observations support the unique direction model for Pb2+ ion displacements, in line with similar relaxor ferroelectric systems near room temperature. Multifield T1 relaxation behavior observed between 9.4 and 21.1 T is indicative of a slowing down of dynamics around 200 K, and appears to be determined by spin-rotation fluctuations at high temperatures and a magnetic-field-dependent relaxation pathway at low temperatures.

Resolution of ambiguity between the depolarization and ferroelectric–relaxor transition temperature through dielectric studies in lead-free perovskite K0.5Bi0.5TiO3

Lead-free relaxor K0.5Bi0.5TiO3 (KBT) has been selected to measure its depolarization temperature (Td) and to establish the difference between the Td and the normal ferroelectric to relaxor transition temperature (TF-R), which is still in a debatable stage for the relaxor ferroelectric system. These parameters are determined separately from the electrically poled specimen through the simple dielectric measurement instead of the pyroelectric measurement or other sophisticated techniques. Albeit, the electric field induces the normal ferroelectric behavior in the nonergodic relaxor state, the relaxor nature appears again through the heating above the freezing temperature. The difference between the frequencies of resonance and anti-resonance peaks in the real part of permittivity remains constant up tõ240 °C, and it reduces to almost zero at ∼285 °C, which has been considered as the Td of KBT. At the temperature higher than Td, an anomaly is noticed in the temperature dependent permittivity as well as in the dielectric loss graph of KBT; this temperature indicates the emergence of the relaxor nature from the normal ferroelectric (TF-R). The Td of the KBT is even higher than some of the lead-free ferroelectrics, which signifies its better suitability for the piezoelectric application. This easy method can be adopted undoubtedly to confirm the Td of the ferroelectric specimen, even for the material of higher Td (above 300 °C).

Reconstructing phase diagrams from local measurements via Gaussian processes: mapping the temperature-composition space to confidence

We show the ability to map the phase diagram of a relaxor-ferroelectric system as a function of temperature and composition through local hysteresis curve acquisition, with the voltage spectroscopy data being used as a proxy for the (unknown) microscopic state or thermodynamic parameters of materials. Given the discrete nature of the measurement points, we use Gaussian processes to reconstruct hysteresis loops in temperature and voltage space, and compare the results with the raw data and bulk dielectric spectroscopy measurements. The results indicate that the surface transition temperature is similar for all but one composition with respect to the bulk. Through clustering algorithms, we recreate the main features of the bulk diagram, and provide statistical confidence estimates for the reconstructed phase transition temperatures. We validate the method by using Gaussian processes to predict hysteresis loops for a given temperature for a composition unseen by the algorithm, and compare with measurements. These techniques can be used to map phase diagrams from functional materials in an automated fashion, and provide a method for uncertainty quantification and model selection.

Enhanced functional response of high temperature stabilized (1-x)PMN-xPT ceramics

Abstract Synthesis of single phase (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics with enhanced electrical response was achieved by excluding excess PbO from the precursor, making them suitable for device applications. This report is an inquiry into the effect of high temperature stabilization used for the realization of single phase PMN-PT ceramics on the electrical properties exhibited by the compositions in the morphotropic phase boundary. Functional response exhibited by the high temperature stabilized ceramics is correlated with the structural fluctuations in the morphotropic phase boundary and the grain pattern observed in the microstructure. Gradual transition from diffuse relaxor ferroelectric system to normal ferroelectric system was also studied. Enhanced ferroelectric response of the composition x=0.35 (Psat=32.03 μC/cm2, Pr=25.11 μC/cm2, EC=6.04 kV/cm, Rsq=1.28, Absolute area=3768, range of electric field=−37 to +37 kV/cm and recoverable energy density= 59.86 mJ/cm3), the improved dielectric behavior of the composition x=0.325 (er(max)=15,703, Tanδmax=0.02 and γ=1.79 (at 1 kHz)) and the high piezoelectric coefficient d33 (390 pC/N and 365 pC/N for x=0.325 and x=0.35 respectively), obtained in the study have confirmed the device worthiness of the synthesized ceramic compositions. This study was carried out to establish that, modulated high temperature synthesis will not deteriorate the electrical properties of the lead based system like PMN-PT, rather will assist the completion of perovskite phase formation, and thus enhance the functional response of the ceramic.

Investigation of morphotropic phase boundaries in PIN–PSN–PT relaxor ferroelectric ternary systems with high Tr-t and Tc phase transition temperatures

New morphotropic phase boundary (MPB) compositions with relatively high Tcs were projected in Pb(In1/2Nb1/2)O3–Pb(Sc1/2Nb1/2)O3–PbTiO3 (PIN–PSN–PT) solid solution based on the perovskite tolerance factor, and were experimentally confirmed. The phase structure, dielectric, pyroelectric, piezoelectric and ferroelectric properties of PIN–PSN–PT ceramics were investigated. The rhombohedral–tetragonal phase transition temperatures Tr-t on the order of 189–210°C, Curie temperatures Tc on the order of 274–285°C and piezoelectric coefficients d33 in the range of 310–360pC/N, were achieved in xPIN– (1−x)PSN–0.37PT (x=0.15–0.23) ceramics, demonstrating a promising relaxor–PbTiO3 system with high phase transition temperatures. In addition, the maps of Tc, Tr-t, d33 and εr with respect to composition were established, based on which, a clear direction for composition screening in future crystal growth of the PIN–PSN–PT system was given.

Dielectric evidence of persistence of polar nanoregions within the ferroelectric phases of (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 relaxor ferroelectric system

The electromechanical and structural properties of [001] and [111]-oriented Pb(Zn1/3Nb2/3)O3-6%PbTiO3 (PZN-6%PT) single crystals have been characterized using dielectric spectroscopy, x-ray diffraction, depolarization current, and piezoelectric techniques from 80 K to 300 K. Both unpoled and poled samples show a dielectric loss peak located in the range from 100 to 200 K. The poled samples show a change in the slope of the real part of the dielectric permittivity and a broad, frequency dependent peak in the imaginary part below 200 K. In the same temperature range, we observed a broadening of the Bragg peaks, fluctuations in the macroscopic polarization, and a change in the rate of decrease in the elastic compliance and the d31 piezoelectric coefficient. These results were analyzed within the framework of three models proposed in the literature. This analysis argues that these observations originate from the freezing of the dynamics of the polar nanoregions (PNRs) at low temperature. This assumption implicates two important results; (i) the PNRs are embedded and persist within the ferroelectric, low-temperature phases, and (ii) they contribute to the large piezoelectric properties of the PZN−x%PT single crystals. These conclusions may be general to all ferroelectric relaxor systems.

Anisotropy of ferroelectric behavior of (1 − x)Bi1/2Na1/2TiO3–xBaTiO3 single crystals across the morphotropic phase boundary

(1 − x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-100xBT) single crystals with three different compositions of x = 0.036, 0.065, and 0.088, covering the rhombohedral to predominantly tetragonal region of the phase diagram and encompassing the morphotropic phase boundary (MPB), were grown by top-seeded solution growth. Dielectric and ferroelectric measurements were performed on samples with different orientations with respect to the crystallographic axes. While the results complied with the current understanding of the crystallographic structure, no enhancement of electromechanical properties based on transient polarization rotation was observed. This clearly sets BNT-100xBT apart from other relaxor ferroelectric systems with a rhombohedral-tetragonal MPB such as (1 − x) Pb(Mg1/3Nb2/3)O3-xPbTiO3. An anomaly was observed in the poling behavior of the strain in 〈001〉 oriented BNT-100xBT in the immediate vicinity of the MPB with x = 0.065, resulting in a giant small-signal piezoelectric coefficient d33 of 4600 pm/V. This effect is hypothesized to be due to an irreversible phase change from rhombohedral polar nanoregions to tetragonal ferroelectric microdomains.

Distinctive contributions to dielectric response of relaxor ferroelectric lead scandium niobate ceramic system

Dielectric properties of (PSN) ceramic system, prepared from mechanochemically activated powder, were studied in a broad temperature range of 150–750 K. Various distinctive contributions were recognized in the detected reponse. A typical relaxor dispersive maximum, accompanied by a sharp dielectric anomaly showing a hysteretic behavior, reveals that developed disordered PSN ceramics undergoes a spontaneous relaxor‐to‐ferroelectric phase transition, even in zero electric field. At high temperatures, a strong dielectric dispersion due to the Maxwell–Wagner‐type contributions of interface layers between the sample and contacts governs the detected response above 500 K. The intrinsic high‐temperature dielectric response follows, however, the universal scaling rather than the classical mean‐field behavior. The latter can be rejected on the confidence level better than 99% according to the F‐test and, furthermore, the analysis revealed a critical exponent that indicates a critical behavior associated with universality classes typically found in spin glasses. Finally, nearly perfect agreement between the fitting parameter of K (obtained by analysis in the interval of 600–775 K) and the experimentally detected value of this relaxor‐to‐ferroelectric phase transition temperature manifests that the low‐temperature fingerprint behavior can be observed at much higher temperatures, well above the dispersive relaxor dielectric maximum.

Influence of the critical point on the electrocaloric response of relaxor ferroelectrics

The electrocaloric effect (ECE), i.e., the conversion of electric energy into heat, is of great importance for application in new generation cooling or heating devices that would be friendlier to the environment. Here, utilizing direct measurements of the ECE change of the temperature ΔT via a high resolution calorimeter, we study the ECE as a function of the magnitude of the electric-field step E in the vicinity of the critical point in several bulk relaxor ferroelectric ceramic systems. Relatively large ΔT of ∼2 to 3 K were obtained at modest fields of 90 kV/cm, even in the case of ceramic materials. The effective responsivity ΔT/E as a function of the electric field shows a characteristic peak near the critical point, which demonstrates the importance of proximity to the critical point for the enhancement of the electrocaloric effect. Experimental results are in good agreement with the theoretical calculations based on the spherical random-bond random-field model.

High temperature lead-free relaxor ferroelectric: Intergrowth Aurivillius phase BaBi2Nb2O9–Bi4Ti3O12 ceramics

Intergrowth BaBi2Nb2O9–Bi4Ti3O12 (BaBi6Ti3Nb2O21) Aurivillius phase ceramic has been found to be a relaxor ferroelectric (RFE) with the highest reported temperature of the maximum of the dielectric permittivity (Tm) of all of the known RFE systems. Dielectric characterization revealed that it has two dielectric anomalies. The first one is a frequency independent broad dielectric constant peak at ∼280 °C, while the second anomaly shows relaxor behavior at 636 °C (100 kHz). There is obvious frequency dispersion of dielectric response at room temperature, which is in agreement with dielectric properties of a typical relaxor. Ferroelectric hysteresis loops and a measurable value of piezoelectric constant d33 confirmed the ferroelectric nature of BaBi6Ti3Nb2O21 ceramics. The piezoelectric response remained even after annealing at temperatures above 636 °C.

Origin of diffuse scattering in relaxor ferroelectrics

High-pressure and variable temperature single crystal synchrotron X-ray measurements combined with first-principles based molecular dynamics simulations study diffuse scattering in the relaxor ferroelectric system PSN (PbSc$_{1/2}$Nb$_{1/2}$O$_3$). Constant temperature experiments show pressure induced transition to the relaxor phase at different temperatures characterized by butterfly and rod shaped diffuse scattering around the $\{$h00$\}$ and $\{$hh0$\}$ Bragg spots, respectively. The simulations reproduce the observed diffuse scattering features as well as their pressure-temperature behavior, and show that they arise from polarization correlations between chemically-ordered regions, which in previous simulations were shown to behave as polar nanoregions. Simulations also exhibit radial diffuse scattering (elongated towards and away from {\bf Q}=(000)), that persists even in the paraelectric phase, consistent with previous neutron experiments on (PbMg$_{1/3}$Nb$_{2/3}$O$_3$) (PMN)

Competing Orders in PZN–xPT and PMN–xPT Relaxor Ferroelectrics

Neutron and x-ray scattering studies on relaxor ferroelectric systems Pb(Zn 1/3 Nb 2/3 )O 3 (PZN), Pb(Mg 1/3 Nb 2/3 )O 3 (PMN), and their solid solutions with PbTiO 3 (PT) have shown that inhomogeneities and disorder play important roles in the materials properties. Although a long-range polar order can be established at low temperature – sometimes with the help of an external electric field; short-range local structures called the “polar nano-regions” (PNR) still persist. Both the bulk structure and the PNR have been studied in details. The coexistence and competition of long- and short-range polar orders and how they affect the structural and dynamical properties of relaxor materials are discussed.

Dynamics of Central Peaks in the Brillouin Scattering Spectra of Relaxor Ferroelectrics

High-resolution Brillouin scattering technique was applied to study the dynamics of central peaks (CPs) in two relaxor ferroelectric systems, PLZT-x/65/35 ceramics and PMN-33%PT [001] single crystals, respectively. It was found that CPs appear very close to an intermediate temperature, Td, for both type of specimens. The temperature dependence of CPs was attributed to the appearance and subsequent growth of polar nanoregions (PNRs) intrinsic to relaxor materials.

Thermal conductivity and heat capacity of the relaxor ferroelectric[PbMg1/3Nb2/3O3]1−x[PbTiO3]x

The evolution of thermal conductivity and heat capacity for the series of ${[{\text{PbMg}}_{1/3}{\text{Nb}}_{2/3}{\text{O}}_{3}]}_{1\ensuremath{-}x}{[{\text{PbTiO}}_{3}]}_{x}$ $(\text{PMN-}{\text{PT}}_{x})$ single crystals with $0\ensuremath{\le}x\ensuremath{\le}1$ are reported. PMN shows typical glasslike behavior in both measurements, which is attributed to the presence of polar nanoregions. With PT doping up to the region of morphotropic phase boundary (MPB), the plateau in thermal conductivity is progressively suppressed. This is reminiscent of partially crystallized glasses and suggests enhanced thermal boundary resistance from ferroelectric domains. The linear temperature contribution and large ${C}_{p}/{T}^{3}$ peak in heat capacity remain nearly constant for PT doping up to the MPB but are rapidly suppressed for larger $x$. These results demonstrate that thermal properties are intimately coupled to the local structures in relaxor ferroelectric systems.

Onset of spontaneous electrostrictive strain below 520 K in Pr-dopedSrTiO3

$Sr_{0.95}Pr_{0.05}TiO_{3}$ ceramic is shown to exhibit anomalous value of cubic lattice parameter at room temperature. A combination of temperature dependent dielectric and synchrotron x-ray powder-diffraction study has revealed that the anomalous lattice parameter has contribution from spontaneous electrostrictive strain that sets in below 520 K. In analogy with the lead-based classical relaxor ferroelectrics, it is suggested that Pr-doped $SrTiO_{3}$ is a new class of high-temperature lead-free relaxor ferroelectric system.